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Old 04-25-2011, 12:54 PM   #1
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Probable Venting Issue


Hello all,

I'm new to posting on this forum, though I've periodically checked it for answers in the past. Unfortunately, right now I have a very specific question that I'm hoping you can help me with.

I am 99% finished a reno of the main bathroom in our house. Without getting into all of the messy details, it's an 80+ year old house, and I ended up gutting the entire bathroom back to the studs (and replaced some of those) and moved the toilet and bathtub to provide a better layout. This shifting led to new drain pipes being installed.

My issue is that now when I drain a full bathtub, it's causing pressure on the toilet. If I let it get to a full-flow drain (i.e., pull the plug from a full tub), I actually get bubbling in the toilet bowl. Reducing the flow (partially pulled plug) reduces this to small waves or no effect (if I drain it really slowly). My best guess is that I've screwed up the venting flow with the new pipes.

Hopefully the drawing I've attached comes through and provides the necessary information. It's not to scale, but should show how the pipes come together. Speaking to this drawing, if I start on the left I've got my main vent pipe running from the basement to the roof. The toilet in the bathroom on the main floor connects directly into this and runs down and out to the city sewer system. The next connection on the main sewage pipe is the bathtub drain pipe that connects into the drain pipe for the sink in the main floor bathroom. The last connection is the toilet from the second floor.

So my questions are:
1) Am I correct in assuming that this is a venting issue?
2) If so, I am wondering if I should replace the 90 degree elbow where the bathtub drain goes vertical leading into the basement with a T-joint, and then connecting into the main vent stack near the ceiling of the 1st floor bathroom (i.e., a horizontal pipe that I enclose with a bulkhead)? Would this fix my problem?
3) Any better/other suggestions?

Thanks,
Tombstone
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Old 04-25-2011, 06:00 PM   #2
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Probable Venting Issue


Bump,
sorry don't have the answer but wanted to keep you "afloat" untill one of the plumbers gets here.

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Old 04-25-2011, 08:04 PM   #3
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Probable Venting Issue


To answer your questions:
1) possibly
2) no, the vent should tie in 6" above the highest fixture on the 2nd floor.

What happens when you flush the top floor toilet? Is the other toilet affected?
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Old 04-25-2011, 08:16 PM   #4
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Probable Venting Issue


Thanks for the reply.

Flushing the upstairs toilet does nothing to affect the downstairs toilet.

In terms of the vent tie-in, I'm a little confused. Based on the old setup, there's no way that the 2nd floor toilet would have tied in at 6" above the highest fixture (assuming you mean where the highest fixture joined the vent pipe).

Also - are you saying that tying into the vent at that point would have NO effect, or would not be the best option?

Thanks in advance for some help. This is really annoying since a) the bathroom reno took a lot longer than expected and b) the problem is completely my own doing/mistake/lack of forethought.
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Old 04-25-2011, 08:42 PM   #5
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Probable Venting Issue


Quote:
Originally Posted by TombstoneDW View Post
Thanks for the reply.

In terms of the vent tie-in, I'm a little confused. Based on the old setup, there's no way that the 2nd floor toilet would have tied in at 6" above the highest fixture (assuming you mean where the highest fixture joined the vent pipe).

Also - are you saying that tying into the vent at that point would have NO effect, or would not be the best option?
Am I understanding your drawing? The upstairs toilet has no vent?
Every fixture should have a vent and they can't (by code) tie into or turn horizontal less than 6" above the rim of the highest fixture. Plumbers use 42" as a rule of thumb, (36" countertop + 6") Tying the vent in the way you propose may work but is not the norm.

Is there a chance you have a partial blockage in your mainline?
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Old 04-25-2011, 09:16 PM   #6
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First, thanks for the reply EPlumber - I appreciate the time you're taking to consider my issue.

I think you're interpreting the drawing correctly, in the sense that the 2nd floor toilet doesn't have a dedicated vent. I ran it vertically down to the basement (about 12 feet) where it jogs and then joins into the main sewage line, which itself is connected to the main vent stack.

My previous thinking was that I should tie the drainpipe of the bathtub into the vent stack along the ceiling of the 1st floor bathroom. Now that I've drawn it out and thought about it, I wonder if I'd be better off cutting in a T about 12" down from the toilet and running a horizontal on IT over to the vent pipe. If my logic is correct, then the draining of the bathtub (which runs past where the 2nd floor toilet joins the mainline) would still pull air from the toilet line, but wouldn't create a vacuum with the inherent trap in the toilet, but go the line of least resistance by pulling from the newly-created vent-stack T-joint. Does this make sense?
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Old 04-25-2011, 09:28 PM   #7
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Sorry - a bit more information.

1) I highly doubt there is a blockage in the main line. Everything is flushing correctly and emptying fine. The problem came about when I actually installed the toilet on the 2nd floor.

2) In terms of "code", I did the plumbing myself, and I take full responsibility for not being up-to-date on the code and what is necessary. I truly appreciate the skill and education required to be a licensed tradesperson, but I enjoy doing things with my own two hands. While a little late, I'm realizing that this may have been a case where I should have acknowledged my own limitations and hired a professional.

3) After rereading your 6"/42" rule I'm still a little confused. The "red" pipes are 4" drain pipes, the purple is 2" and the blue (light and dark) are the vent stack/main sewage line. The gray lines represent walls/floor joists - this picture is a cross-section of my two bathrooms (1st and second floor) and the basement. The toilet on the second floor goes completely vertical from the flange to the basement. Does that help?
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Old 04-25-2011, 09:59 PM   #8
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I am in no way a plumber, just want to get that out of the bag.


I am in the same process as you are. I am redoing my second floor bathroom. My house is 60 years old. The way it was setup is ther only vent in the main stack coming out of the roof. This stack vents 3 sinks, 3 toliets, and a tub. This is considered "wet venting", which is when your vent is another fixture's drain.

Per code each fixture should have it's own vent.


As others have suggested, I would add a 2" pipe within 6' of the tub and run it up into the second fllor. You can either run it out of the roof or into the main stack once you get to the 6" highest fixture rule.

if you come out of the roof with it, keep in mind some places require different size pipes being used due to frosting over. In my area, you are required to use 4" on all pipes coming out of the roof.

If you do go to the trouble to add the vent, I would add one to every fixture including the toliet.


You should be able to make a "header", which all of the vent lines meet in one place and the just run 1 pipe up.


I have attached a picture that I made for my remodel. The basement and 1st fllor won't be to code ATM. But if you look at the second floor, all of the blue pipes are purely vents(will never see water).


Again, not a plumber, just someone in the same boat as you. This is what I have read from my reading prior to diving in.


Brian
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Old 04-25-2011, 11:05 PM   #9
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beamar,

Thanks for the advice. I'm worried that I'll have to reopen the second floor bathroom - something I'd like to avoid doing.

Unfortunately it seems like all of the recommendations thus far are suggesting that this is not possible. To avoid this issue, I'd need to connect either the toilet (4") or the bathtub (2") into the vent pipe at about 10" below both, and closer to 50" below the sink.

Doing so would clearly be against code, but I guess my question is whether this would be functionally appropriate - i.e., would it solve the issue? The reason I ask is that in the old piping, everything would have been about 4' below the sink (as all connections were in the floor?
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Old 04-25-2011, 11:18 PM   #10
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A cheap/easy fix that will help is an Air admittance valve. They aren't allowed in some places. Also they can Freeze close if installed in locations that leave it acceptable to freezing temps.
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Old 04-25-2011, 11:37 PM   #11
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Your best solution- and I know you don't want to hear this- the tub and toilet need to be vented through the roof or tied into the original vent stack(see beamar's drawing). These vents need to be above the fixtures.
The codes that plumbers follow have been developed from years of field study and some short cuts can be taken which will work sometimes. But I advise against it.
As suggested, AAV's are a available. They might be your best choice.
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Old 04-26-2011, 06:26 AM   #12
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I appreciate the advice. I have one more question. I was thinking about this a little more, and I think you're right - there may have been a 2" connection into the vent pipe well above the floor in the bathroom that vented the sink and tub previously.

I've updated my drawing below - would it be equivalent to your suggestion if I extend the pipe and connect in this way? That is, run the pipe across the top of my downstairs bathroom and tie into the 2", not the vent pipe? The length will be about 5' from the bathtub.
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